There are a number of stations that have been assigned a pair of channels, consisting of one National Television System Committee (NTSC) channel and one digital (DTV) channel, that require the station to transmit both NTSC and DTV channels at their maximum effective radiation power (ERP), for example, 5 megawatt (MW) for NTSC channels and 1 MW for DTV channels.
Often, it is an objective to direct transmission of NTSC and DTV signals in a particular direction. Conventionally, single-slot coaxial antennas, which have a single slot cut into the wall of the antenna, are utilized to transmit directional signals. When directional signals are transmitted, the majority of signal power is transmitted in one direction, and “skull” or “cardioid” shaped azimuth patterns are generated.
However, conventional single-slot antennas are at least sometimes not successful in transmitting high power signals, in particular, two high power channels, such as a 5 MW NTSC channel and a 1 MW DTV channel, at the same time. Conventional single-slot antennas are at least sometimes unable to adequately dissipate the amount of energy that is attributed to the pair of channels.
“Q” is a ratio that characterizes the amount of energy that is stored at a slot of an antenna versus the amount of energy that is dissipated by the slot. Ideally, an antenna operates more efficiently when it avoids the storing of energy. Typically, the higher the “Q” of a slot, the less power the slot of the antenna is able to handle. If the amount of energy stored at a slot becomes excessive, the air between the slot may begin to ionize, and the slot may function improperly.
It is known in the art that coaxial antennas with multiple slots have a lower “Q” per slot. In general, the more slots cut into a coaxial wall of an antenna layer, the more the antenna is able to dissipate the energy it receives. However, coaxial antennas with multiple slots have traditionally been utilized to generate omni-directional azimuth patterns. When more than one slot is cut into a layer of conventional coaxial antenna, the coaxial antenna will transmit energy, substantially evenly, in more than one direction. While conventional multiple-slotted coaxial antennas are successful in reducing the “Q” of an antenna, they have generally not been successful in transmitting directional signals.
Accordingly, it would be desirable to provide an antenna that avoids at least to some extent the storing of energy at a slot.
It would also be desirable to provide an antenna that is capable of transmitting high power NTSC and DTV channels simultaneously.
It would also be desirable to provide a directional slotted antenna.